Tutorial: Modeling Liquid Reactions in CIJR Using the Eulerian PDF transport (DQMOM-IEM) Model Introduction The purpose of this tutorial is to demonstrate setup and solution procedure of liquid chem- ical reactions using the Eulerian Composition PDF transport model with Discrete Quadra- ture Method of Moments (DQMOM) in ANSYS FLUENT. For reactions involving liquids, mixing at molecular level- termed as micromixing, plays a significant role in determining the conversion of products. In cases where there are parallel competing reactions, the micromixing can singularly affect the yield of the desired product. Fast chemistry models in ANSYS FLUENT like Non-premixed equilibrium model, steady laminar flamelet and eddy dissipation model cannot capture the physics of micromixing and thus may not predict conversion, selectivity and scale-up accurately. While the Full composition PDF transport is well equipped to solve liquid reactions, the computation cost involved with the lagrangian approach is very high since kinetic calculations are performed using particle based methods (Monte-carlo methods) which are computationally intensive. The DQMOM-IEM model solves for the PDF transport in Eulerian framework, this sig- nificantly reduces the computational cost involved while preserving the accuracy of the calculations. This tutorial demonstrates how to do the following: • Set up liquid chemical reactions in a confined impinging jet reactor. • Set up DQMOM-IEM PDF Transport model with liquid micro-mixing extension. • Calculate the solution.. • Examine results using graphics. Prerequisites This tutorial is written with the assumption that you have completed Tutorial 1 from the ANSYS FLUENT 14.5 Tutorial Guide, and that you are familiar with the ANSYS FLUENT navigation pane and menu structure. Some steps in the setup and solution procedure will not be shown explicitly. A good understanding of turbulence and species mixing/reaction, as well as their modeling is desirable. c ANSYS, Inc. December 4, 2012 1
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Tutorial: Modeling Liquid Reactions in CIJR Using the
Eulerian PDF transport (DQMOM-IEM) Model
Introduction
The purpose of this tutorial is to demonstrate setup and solution procedure of liquid chem-ical reactions using the Eulerian Composition PDF transport model with Discrete Quadra-ture Method of Moments (DQMOM) in ANSYS FLUENT.
For reactions involving liquids, mixing at molecular level- termed as micromixing, plays asignificant role in determining the conversion of products. In cases where there are parallelcompeting reactions, the micromixing can singularly affect the yield of the desired product.Fast chemistry models in ANSYS FLUENT like Non-premixed equilibrium model, steadylaminar flamelet and eddy dissipation model cannot capture the physics of micromixingand thus may not predict conversion, selectivity and scale-up accurately. While the Fullcomposition PDF transport is well equipped to solve liquid reactions, the computation costinvolved with the lagrangian approach is very high since kinetic calculations are performedusing particle based methods (Monte-carlo methods) which are computationally intensive.The DQMOM-IEM model solves for the PDF transport in Eulerian framework, this sig-nificantly reduces the computational cost involved while preserving the accuracy of thecalculations.
This tutorial demonstrates how to do the following:
• Set up liquid chemical reactions in a confined impinging jet reactor.
• Set up DQMOM-IEM PDF Transport model with liquid micro-mixing extension.
• Calculate the solution..
• Examine results using graphics.
Prerequisites
This tutorial is written with the assumption that you have completed Tutorial 1 from theANSYS FLUENT 14.5 Tutorial Guide, and that you are familiar with the ANSYS FLUENTnavigation pane and menu structure. Some steps in the setup and solution procedure willnot be shown explicitly. A good understanding of turbulence and species mixing/reaction,as well as their modeling is desirable.
Modeling Liquid Reactions in CIJR Using the Eulerian PDF transport (DQMOM-IEM) Model
Problem Description
A confined impinging-jets reactor (CIJR) consists of two high-velocity, coaxial liquid jetsthat collide and produce mixing times on the order of milliseconds. In this tutorial, thefollowing pair of second- order parallel reactions is employed to evaluate the extent ofmixing.
The first reaction is very fast (K1 = 1.4E8m3/mol.s), and the second is very slow (K2 =643E − 3m3/mol.s). When the liquid micro-mixing model is enabled, ANSYS FLUENTinterpolates the mixing constant used in IEM model from model turbulence and scalarspectra. A diagram of the CIJR with two reactants impinging at the center of the reactoris shown in Figure 1.
The solution will be performed in two stages:
Figure 1: Problem Schematic
Preparation
1. Copy the mesh file, dqmom.msh.gz to the working folder.
2. Use FLUENT Launcher to start the (3D) version of ANSYS FLUENT.
Modeling Liquid Reactions in CIJR Using the Eulerian PDF transport (DQMOM-IEM) Model
Setup and Solution
Step 1: Mesh
1. Read the mesh file, dqmom.msh.gz.
File −→ Read −→Mesh...
As the mesh file is read, ANSYS FLUENT reports the progress in the console.
Figure 2: Mesh Display
Step 2: General Settings
1. Retain the default settings.
General
2. Check the mesh.
General −→ Check
ANSYS FLUENT performs various checks on the mesh and reports the progress inthe console. Pay attention to the minimum volume reported and make sure this is apositive number. Scaling is not required for this case.
Modeling Liquid Reactions in CIJR Using the Eulerian PDF transport (DQMOM-IEM) Model
2. Define species model.
Models −→ Species −→ Edit...
(a) Select Composition PDF Transport from the Model list.
The dialog box will expand after the selection.
(b) Select Eulerian in the PDF Transport Options group box.
(c) Enable Volumetric in the Reactions group box.
(d) Enable Liquid Micro-Mixing in the Options group box.
(e) Click OK and close the Species Model dialog box.
At this stage, ANSYS FLUENTrequires the chemical mechanism which containsthe species, their properties, and kinetics. Since these have not been provided anError dialog box is displayed.
(f) Click OK to close the Error dialog box.
An information dialog box will open reminding you to confirm the property val-uesthat have been extracted from the database.
Modeling Liquid Reactions in CIJR Using the Eulerian PDF transport (DQMOM-IEM) Model
(g) Click OK to close the Information dialog box.
Step 4: Materials
The DQMOM model requires the mixture materials to be setup. This is done by creatingthe species participating in the reactions and then by adding them to the mixture specieslist.
Materials −→ Create/Edit...
1. Add water to the material list.
(a) Click Fluent Database to open the Fluent Database Materials dialog box.
(b) Select fluid under Material Type drop-down list.
(c) Select water-liquid (h2o<l>) from the Fluent Fluid Materials list and click Copy.
(d) Close the Fluent Database Materials dialog box.
Modeling Liquid Reactions in CIJR Using the Eulerian PDF transport (DQMOM-IEM) Model
2. Set the solution controls.
Solution Controls
(a) Enter 0.8 for Eulerian PDF in the Under-Relaxation Factors group box.
(b) Click Equations... and de-select Energy from the equations list.
(c) Click OK to close the Equations dialog box
Note: Energy equation is enabled by default for species model with reactions. Howeverfor your case the flow is isothermal. The densities are also constant. Thereforesolving for energy is not necessary.
Modeling Liquid Reactions in CIJR Using the Eulerian PDF transport (DQMOM-IEM) Model
3. Set the convergence limits.
Monitors −→ Residuals −→ Edit...
(a) Enter 1e-4 for fmean, a, b, d, and p3.
(b) Enter 5e-4 for p1 and p2.
(c) Click OK and close the Residual Monitors dialog box.
4. Initialize the solution.
Solution Initialization −→ Initialize
Hybrid Initialization is the default Initialization Method in ANSYS FLUENT 14.5. Referto the section 28.11 Hybrid Initialization, in the ANSYS FLUENT 14.5 User’s Guide.